-LRB- CNN -RRB- -- Rail experts Tuesday questioned the effectiveness of one step being taken by New York 's Metro-North Railroad to ensure safety one week after the derailment of a speeding commuter train killed four people and injured dozens of others .

The Metropolitan Transportation Authority , which operates the railroad , said late Sunday that `` alerter '' systems -- which require engineers to respond to alerts , sound an alarm if they are unresponsive and eventually brake the train in an emergency -- will be installed in every operator cab within the next year . Currently , such systems in the engineer 's position are present in two-thirds of the railroad 's fleet .

The Hudson line train that derailed on December 1 had an alerter system in the engine car at the rear but not in the front cab , where the engineer apparently nodded off at the controls as the train approached a curve at 82 miles per hour . The engineer 's lawyer and union representatives said the train 's hypnotic motion may have caused him to nod off -- a case of what the lawyer termed `` highway hypnosis . ''

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Steven Harrod , a University of Dayton professor and expert on railway operations , said the effectiveness of `` alerter '' systems is debatable .

`` It 's not the cure all for all problems , '' he told CNN . `` Research has been done showing that some crews are adapting to these ` alerters ' and they 're still sleeping to the ` alerters . ' It 's that whole highway hypnosis thing . ''

A 2007 study of `` alerter '' technology by Massachusetts Institute of Technology said , `` Engineers can become inattentive and keep hitting the alerter even when nodding off . ` Alerter naps ' has become a commonly used term . ''

The study cited a 2006 National Transportation Safety Board investigation report on a freight train collision in Macdona , Texas , in which escaping liquified chlorine ultimately killed the conductor and two local residents . The study said the engineer experienced what it called `` alerter naps '' in which he `` apparently drifted in and out of micro-sleep . ''

`` I view the alerter devices as being only partially effective , '' Steven Ditmeyer , a former Federal Railroad Administration official who teaches at Michigan State University , said in an e-mail . `` During my years in the railroad industry , there have been numerous occasions when locomotive engineers have responded to alerter alarms while being in less than a fully conscious state . ''

While two-thirds of Metro-North 's operating fleet is equipped with alerters in the engineer 's position , the remaining one-third is equipped with `` dead man '' controls , another safety measure which theoretically requires the conductor make continuous conscious input to keep the train running .

At the time of the accident , the train was in `` push mode , '' meaning that the locomotive was in the rear of the train pushing it along the tracks , with engineer William Rockefeller in a cabin at the front operating it remotely . His cabin was equipped with a `` dead man pedal '' that required constant downward pressure with the foot to keep the train moving , the MTA has said . The dead man pedal was working properly , authorities said .

The newer model locomotive in the rear , however , was equipped with an alerter system which sounds a tone every 25 seconds , requiring the engineer to respond with a tap within 15 seconds while the train is in steady motion .

Late Sunday , the MTA said it was taking additional safety measures : Signal crews installed new protections at the bend near the Spuyten Duyvil station in the Bronx -- where the fatal derailment occurred -- to warn engineers of the speed reduction and automatically apply emergency brakes if speed is not lowered to 30 mph .

By Tuesday morning , the MTA said , Metro-North also enhanced communication between engineers and conductors to ensure trains are operated at safe speeds at four other critical curves and five movable bridges . Conductors will stand with engineers at the control cab through the critical curves or they will communicate by radio .

On Monday , the NTSB continued to rule out mechanical causes in a deadly crash while adding to the possibility that human error was involved . The NTSB said it has completed its inspection of the train and found no anomalies .

The board found no problems with speed sensors , the brake control unit or the train 's propulsion controller .

At 7:11 a.m. that Sunday -- about 11 minutes before the derailment -- the engineer did not dim the train 's headlights as required when it passed another train , the NTSB said Monday .

It also said it believes that positive train control , a costly , high-tech system that targets human error , could have prevented the crash . The safety board has pushed the system for about 20 years . Congress is requiring most major railroads , including Metro-North , to install the costly systems by the end of 2015 .

David Rangel , an instructor at the Modoc Railroad Academy in Marion , Illinois , advocates putting another person in the engineer 's cab of commuter trains , a practice that is common in freight trains and airplane cockpits .

`` It will increase the cost , of course , but the alternative that the railroads are looking at , and the federal government is trying to force on the railroads , positive train control , is certainly much more costly , '' Rangel told CNN . `` We 're into the hundreds of millions of dollars right now and we have n't even had the implementation of that system . ... The problem here is that we are dealing with humans in the cabs of those locomotives and we have frailties . ''

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Rail experts question a step taken to make trains safer after Metro-North wreck

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Authorities are requiring `` alerters '' in every operator cab by end of 2015

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Expert : `` Alerter devices ... only partially effective ''